The primary structural component of a bicycle is the bicycle frame. Typically, the bicycle frame comprises an elongate top tube which is rigidly secured to and extends between a head tube and a seat tube. The head tube typically provides a structural base for the stem of the bicycle to which the handlebars are attached. The seat tube provides a base for a seat post which is generally telescopically received therewithin and to which is secured the saddle or seat of the bicycle. In typical bicycle frame construction, the seat tube includes a generally cylindrical axle-receiving bracket attached to the bottom end thereof which is adapted to receive a bottom bracket axle. The bottom bracket axle typically extends between and interconnects the cranks to which are attached to the pedals. Rigidly secured to and extending between the head tube and the cylindrical axle-receiving bracket is an elongate down tube.
In addition to the aforementioned structural components, rigidly secured to and extending rearwardly from the axle-receiving bracket are first and second chain stay members. Additionally, rigidly secured to and extending downwardly from the upper end of the seat tube are first and second seat stay members having lower ends which are rigidly secured to the back ends of respective ones of the first and second chain stay members. Typically, the lower ends of the seat stay members and the back ends of the chain stay members are attached to respective ones of a pair of drop-outs which are adapted to receive the rear tire axle of the rear wheel. The head tube, seat tube, top tube, and down tube are typically secured to each other and to the axle-receiving bracket in a manner defining a main front triangle portion of the bicycle frame. The seat stay and chain stay members, when connected to the seat tube, axle-receiving bracket, and drop-outs, typically define a back triangle portion of the bicycle frame.
The foregoing description generally represents the construction of conventional prior art bicycle frames. Typically, when such prior art frames are constructed, the aforementioned structural components are rigidly secured to each other through the use of welding or brazing techniques. Though this method of constructing the bicycle frame provides the resultant frame with structural integrity, the bicycle frame does not possess a suspension having shock absorbing characteristics. As will be recognized, the ride, comfort, and performance of the bicycle would be greatly enhanced if the bicycle frame were adapted to at least partially accommodate the shocks routinely encountered while riding the bicycle.
In recognition of the desirability of accommodating the shocks routinely encountered while riding the bicycle, prior art bicycle frames have been developed which include front and/or rear shock absorbing assemblies. However, such prior art bicycle frames, though having shock absorbing capabilities, possess certain deficiencies which detract from their overall utility. In this respect, such bicycle frames typically include multiple pivot joints, each of which generally comprises a pivot pin which extends through corresponding apertures formed at the ends of frame members of the bicycle frame which are to be pivotally connected to each other.
Though such construction provides for pivotal movement along a desired axis, it necessitates the forming apertures at the ends of the frame members which are to be joined to each other. Each aperture must be machined into a solid member or lug which is typically welded to the tubularly configured frame member. The solid members or lugs are secured to each of the tubular frame members to be joined so as to define a clevis. As will be recognized, such construction methodology inherently requires precision tooling and skilled labor. Thus, pivoting joints formed in accordance with such contemporary methodology are costly and comparatively difficult to fabricate. Such prior art pivoting joints also have an inherent requirement for maintenance such as cleaning and lubrication. These prior art pivoting joints are also susceptible to contamination, particularly since bicycles are commonly used in environments where they are exposed to various environmental contaminants such as dirt, sand, debris, etc.
As such, there exists a need in the prior art for a flexible joint for a bicycle frame which facilitates the resilient bending or flexion of the frame members interconnected thereby about a single desired axis, while mitigating the resilient bending or flexion of such frame members about all other axes, as well as mitigating torsional movement of the interconnected frame members relative to each other. The flexible joint constructed in accordance with the present invention is also adapted to eliminate the need for substantial maintenance, and is inexpensive to manufacture, thus facilitating easy assembly of the bicycle frame.